This invention relates generally to a ventilator therapy apparatus and method utilizing an inhalation heater and is an improvement over the system disclosed in my prior copending application, Ser. No. 89,320 filed Oct. 30, 1979 now U.S. Pat. No. 4,248,217, with respect to which the present application is a continuation-in-part.
According to the disclosure in my aforementioned prior application, a plural mode type of control system for an inhalation heater is operative only in its tracking mode to so regulate the temperature of the inspired air to track below the temperature of the expired air by a substantially constant amount. The objective of such tracking was to prevent the patient from absorbing heat through the respiratory system in excess amounts that may cause heat stress. Toward that end, temperature sensors were provided for measuring the temperature of both the inspired gas and the expired gas without any direct measurement of body core temperature. Further, in the automatic tracking mode of operation, the inspired gas temperature is tracked only below the expired gas temperature by a substantially constant amount. The foregoing system was based on the heating of the gas by the body after it is inhaled under control of the body's temperature regulating system.
It is well known in the art that during Stage III, Plane III anesthesia, the most common level of anesthesia for major surgery, the body's temperature regulating system is non-functional. Therefore, during long surgical procedures, the patient's body tends to cool down below normal body temperature. This condition can cause serious medical problems in the surgical recovery area and the heater control system disclosed in my prior copending application would not be capable of coping with such a condition.
It is, therefore, an important object of the present invention to provide an improved heater control system for inhalation heaters through which the patient's body temperature may be substantially maintained at a desired level determined by the anesthesiologist despite any malfunction of the body temperature regulatory system of the patient.